The present exemplary embodiments relate to media (e.g., document or paper) handling systems and systems for printing thereon and is especially applicable for printing systems comprising a plurality of associated marking engines or image output terminals (“IOTs”).
The subject application is related to the following co-pending applications: U.S. Ser. No. 10/924,113, for “Printing System with Inverter Disposed For Media Velocity Buffering and Registration”;                U.S. Ser. No. 10/924,459, for “Parallel Printing Architecture Consisting of Containerized Image Marking Engine Modules”; and        U.S. Ser. No. 10/924,458, for “Print Sequence Scheduling for Reliability”.        
Printing systems including a plurality of IOTs are known and are generally referred to as tandem engine printers or cluster printing systems. See U.S. Pat. No. 5,568,246. Such systems facilitate expeditious duplex printing (both sides of a document are printed) with the first side of a document being printed by one of the IOTs and the other side of the document being printed by another so that parallel printing of sequential documents can occur. The document receives a single pass through the first IOT, is inverted and then a single pass through the second IOT for printing on the second side so effectively the document receives a single pass through the system but is duplex printed. Single pass duplex printing can be much faster than duplex printing in a single IOT.
However, the system must also be capable of simplex (one-sided) printing. In this case, if the document were printed on the one side at the first IOT, then transported through a second sequential IOT, its transport would consume the transport path through the second IOT with no printing purpose but delivery to a finishing module. Use of the second IOT as merely a transport path is an inefficient use of the module when it could be parallel printing sheets along with the first IOT. Another aspect of such inefficiency is that an IOT has a limit to transport speeds through the image transfer zone of the IOT, which transport speed is usually slower than a document can be transported through other portions of the system.
Especially for parallel printing systems, architectural innovations which effectively preclude non-marking transport through an IOT can enhance document process path reliability and increase system efficiency.